Lung cancer is a leading cause of cancer-associated mortality in the majority of countries (1), including China (2). Non-small cell lung cancer (NSCLC) constitutes 82% of all incidences of lung cancer (3). Pathologically, genetic and environmental interactions serve a key role in the development and progression of lung cancer (4). It is biologically possible that host genetic susceptibility is a factor in the development of lung cancer, and contributes to the variation in individual cancer risk (5).

Human carbonyl reductase 1 (CBR1) is ubiquitously expressed NADPH-dependent enzymes belonging to the short dehydrogenase/reductase (SDR) family, which is involved in catalyzing the conversion of various endogenous and xenobiotic carbonyl compounds to their respective alcohol derivatives (6). CBR1 is also hypothesized to participate in cellular processes such as signal transduction (7), apoptosis (8), carcinogenesis (9) and drug resistance (10), and serves an important role in endometrial cancer (11), acute myeloid leukemia (12) and hepatocellular carcinoma (13). Schlager and Powis (14) reported that the level of CBR1 activity was significantly increased in lung tumors compared within normal tissue. Numerous studies have provided evidence that gene polymorphisms may influence the susceptibility to NSCLC (15,16). A study in the USA has identified that genetic polymorphisms of the CBR1 gene, rs3787728 and rs2835267, are associated with susceptibility to lung cancer (17). Although the USA and China are similar in certain ways, the living environment and ethnic background of the population is also different in some ways. In the present study, the association between rs3787728 and rs2835267, single-nucleotide polymorphisms (SNPs) of CBR1, and the NSCLC risk of the Chinese population was investigated, and the impact of these SNPs on susceptibility and clinicopathological characteristics of NSCLC was evaluated.

A total of 500 patients, consisting of 350 males and 150 females, and 500 healthy controls, consisting of 259 males and 240 females, with gender information for 1 control subject missed, were of Chinese Han origin. A total of 280 male and 21 female patients were smokers or former smokers, where as 189 male and 14 female controls were smokers or former smokers. A total of 1,000 participants, 331 with adenocarcinoma (ADC), 169 with squamous-cell carcinomas (SCC) and 500 healthy controls were successfully genotyped for rs3787728 and rs2835267 polymorphisms of CBR1. The studied population was within HWE, P=0.86506 for rs3787728 and P=0.54904 for rs2835267.

The association between allele frequency in rs3787728 and rs2835267 CBR1 and the clinicopathological parameters and gender of patients with NSCLC was analyzed and is presented in Tables I–III. The allele frequency in rs3787728 was significantly different between the patients with NSCLC and the controls (OR=1.209; 95% CI=1.013–1.442; P=0.0349), and was also significantly different between male patients with NSCLC and male controls (OR=1.278; 95% CI=1.016–1.607; P=0.0358). The thymine (T) allele in rs3787728 was observed to be associated with an increased risk for NSCLC development, particularly for the development of NSCLC in males. With respect to allele frequencies in rs2835267, no statistical differences were observed between the case and control subjects (P=0.4595). With respect to allele frequencies in rs2835267, no statistical differences were observed between male NSCLCs and male controls (P=0.6842), between female NSCLCs and female controls (P=0.4897), between patients with ADC and the controls (P=0.3566), or between patients with SCC and the controls (P=0.9059).

The association of the genotype frequency of rs3787728 and rs2835267CBR1 with the clinicopathological parameters and gender of patients with NSCLC was analyzed and is presented in Tables IV–VI. Logistic regression analysis revealed that the rs3787728 T/T allele homozygote was associated with an increased risk of NSCLC in all patients (OR=1.382; 95% CI=1.019–1.875; P=0.037), and patients exhibiting the rs3787728 T/T major allele homozygote exhibited a 1.537-fold greater risk in developing lung SCC (95% CI=1.019–2.318; P=0.0395). However, the rs3787728 cytosine (C)/C allele homozygote was associated with a decreased risk of ADC in male patients (OR=0.633; 95% CI=0.413–0.969; P=0.0348). There was no statistical difference with respect tothe CBR1 rs2835267 SNP genotype between the patients with NSLCLC and the controls, between patients with ADC and the controls, or between patients with SCC and the controls (P>0.05). With respect to genotype frequencies in rs2835267, no statistical differences were observed between male NSCLCs and male controls (T/T vs. C/C+C/T, P=0.3768; C/C vs. T/T+C/T, P=0.5966) or between female NSCLCs and female controls (T/T vs. C/C+C/T, P=0.7844; C/C vs. T/T+C/T, P=0.3456).

The present study assessed the association between the CBR1 SNPs rs3787728 and rs2835267 and the risk of developing NSCLC, and identified that patients with the rs3787728 T allele exhibited an increased risk of developing NSCLC, particularly male patients with NSCLC. The CBR1 rs3787728 T/T allele homozygote was associated with a higher risk for NSCLC and lung SCC in all patients, and the C/C allele homozygote was associated with a lower risk for ADC in male patients. However, the present study identified a lack of association between the polymorphisms of CBR1 rs2835267 with NSCLC, regardless of whether the NSCLC was of SCC or ADC type.

In humans, CBR1 is known as prostaglandin 9-ketoreductase (PG-9-KR) which inactivates prostaglandin E2 (PGE₂) and other prostaglandins (18,19). PGE₂ serves an important role in inhibiting apoptosisand inducing angiogenesis (20). The inactivation of PGE₂ by CBR1 may inhibit cancer angiogenesis (21), which serves an important role in the growth, progression and metastasis of cancer (22). A significant correlation between reduced CBR1 mRNA expression and active angiogenesis has been identified (21). Previous studies have revealed that CBR1 serves an important role in the metastasis of cancer cells by decreasing PGE₂ levels (19,21).

In addition, CBR1 reduces numerous xenobiotic carbonyl substrates to the corresponding alcohol metabolites (23). Analyses of the >7,000 compounds in cigarette smoke have identified ~70 carcinogens (24), the majority of which require metabolic activation to exert their cancer-causing effects (25). 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) and benzo(a)pyrene [B(a)P] are xenobiotic substrates of CBR1 (23), which are present in tobacco and tobacco smoke (26,27). NNK and B(a)P are theorized to serve important roles in human tobacco-associated cancer (25). CBR1 activity serves plays a role during the metabolism of NNK in human lungs (26). B(a)P may upregulate the expression of CBR1 in human lung tissues and lung cancer cells via the aryl hydrocarbon receptor pathway (23). Individual susceptibility to lung cancer may be affected by polymorphisms in genes such as CBR1, which encode proteins responsible for the detoxification of carcinogens in cigarette smoke (23). CBR1 polymorphisms may affect thebalance of activation vs. detoxification of NNK and B(a)P, thus increasing vulnerability or protection to the lungs of smokers (23).

In accordance with the aforementioned previous studies, the present study indicated that CBR1 may be a susceptibility gene involved in the development of NSCLC. In the present study, the individuals with CBR1 rs3787728 T/T homozygote exhibited a 1.382-fold increased risk for developing NSCLC and a 1.537-fold increased risk for developing lung SCC, compared with the C/C homozygote or T/C heterozygote individuals. However, C/C homozygote individuals exhibited a 0.633-fold decreased risk for developing lung ADC. Notably, the CBR1 rs2835267 polymorphism itself was not associated with the risk of developing NSCLC, contrary tothe results of study by Modesto et al (17). These differences may be attributed to the distinct genetic background and the different living environments of the Chinese population compared with other populations.

To conclude, the present study identified that CBR1 rs3787728 polymorphisms are significantly associated with NSCLC in Chinese people. However, the small sample size may be a limitation of the present study; in addition, population stratification may have led to a bias. Additional studies are required to elucidate the functional impact of CBR1 expression and activity in NSCLC.